Substrates for information recording media, particularly glass substrates as substrates for magnetic disks, are widely used, and commercially available glass is known which has a composition comprising, as represented by mol %, 65.4% of SiO2, 8.6% of Al2O3, 12.5% of Li2O, 10.5% of Na2O and 3.0% of ZrO2. This commercially available glass is subjected to chemical strengthening treatment before use.
On the other hand, glass A for a magnetic disk substrate has been proposed which may or may not be subjected to chemical strengthening treatment (Patent Document 1). This glass A comprises, as represented by mol %, from 61 to 66% of SiO2, from 11.5 to 17% of Al2O3, from 8 to 16% of Li2O, from 2 to 8% of Na2O, from 2.5 to 8% of K2O, from 0 to 6% of MgO, from 0 to 4% of TiO2 and from 0 to 3% of ZrO2, wherein Al2O3+MgO+TiO2 is at least 12%, Li2O+Na2O+K2O is from 16 to 23%, and in a case where B2O3 is contained, its content is less than 1%.
Meanwhile, in a process for producing a glass substrate, polishing is, in many cases, carried out by means of a slurry containing cerium oxide abrasive grains. For example, in the production of a glass substrate to be used for an information recording medium such as a magnetic disk, the main surface and the edge surface of a glass disk cut out from a glass plate, are polished by means of a slurry containing cerium oxide abrasive grains, and then, in order to further planarize the main surface, final polishing may be carried out by means of a slurry containing colloidal silica abrasive grains. At that time, even if cerium oxide abrasive grains may remain on the main surface, they will be removed by the final polishing, but cerium oxide abrasive grains attached to the edge surface are likely to remain without being removed, and in a cleaning step after the final polishing, they are likely to re-deposit on the main surface to constitute product defects.
Under such backgrounds, it is desired to completely remove cerium oxide abrasive grains, and a cleaning liquid containing an inorganic acid and a reducing agent has been proposed (e.g. Patent Documents 2 and 3). In this proposal, it is said that cerium oxide abrasive grains are dissolved and removed by the action of the inorganic acid and ascorbic acid.
Further, it has been also proposed to use a cleaning liquid containing heated sulfuric acid as the main component, in the cleaning of the final step (e.g. Patent Document 4).